1. Field of the Invention
This invention relates to flexible hydraulic hose, and more particularly to hydraulic hose that can withstand high pressure, maintain flexibility, resist kinking, is economical to produce, and is resistant to cut through and burn through.
2. Description of the Prior Art
Flexible hoses made of elastomeric or flexible plastic materials require reinforcement by material such as braided, helically wound, or knitted filaments of rayon, Dacron, steel wire, or the like when the hoses are to be used for conveying fluids under high pressure, such as hydraulic pressures over 1,000 psi. More than one layer of reinforcement material is often required to provide the burst strength needed for high pressure applications.
When two or more layers of reinforcement material are used, several problems arise. If a fibrous non-metallic material such as Nylon 6/6, Dacron, rayon or the like is used as the reinforcement material, there may be substantial elongation of the reinforcement material filaments and expansion in hose diameter when the hose is under pressure. These fibrous non-metallic materials impart a reduced level of strength when compared to steel wire. In addition, a hose using these reinforcement materials is not always sufficiently resistant to kinking, cut through by sharp objects or burn through by flame or heat.
In contrast, if metal wire is used as the reinforcement material, the hose is highly resistant to kinking, cut through, and burn through. However, when multiple metal wire layers are used as reinforcement material the use of a buffer layer of thermoplastic or elastomeric material is typically needed to act as a cushion to resist abrasion of the wire layers during pressure loading, thus adding to manufacturing cost and complexity. Still another problem with multiple metal wire braid hose is pinhole type failures during high pressure impulse occurrences.
Another approach has been suggested to use a hose structure using a reinforcement comprising two layers of an aromatic polyamide or "aramid" yarn that is available from the E. I. duPont de Nemours Company under the trademark Kevlar and which was formerly designated by duPont as Fiber B Nylon. The layers of Kevlar would replace the other reinforcement layers used in the prior art. The use of two layers of Kevlar reinforcement would result in a relatively flexible hose having a very high burst strength and which can dissipate some shock pressures without causing system sluggishness. This hose construction, however, suffers from the fact that it is not resistant to cut through and has reduced kink resistance. Additionally the Kevlar yarn is relatively brittle and also expensive.